Line narrowing of molecular fluorine laser emission

ABSTRACT

A molecular fluorine laser system includes a discharge tube filled with a gas mixture including molecular fluorine and at least one buffer gas and having a total pressure of less than substantially 2500 mbar, multiple electrodes within the discharge tube, a pulsed discharge circuit connected to the electrodes for energizing the gas mixture, a line-selection optic for selecting one of multiple closely-spaced lines around 157 nm emitted from the discharge tube, and a laser resonator including the line-selection optic and the discharge tube for generating a beam of laser pulses having a wavelength around 157 nm at a bandwidth of less than 0.6 pm.

[0001] This application claims the benefit of priority to U.S.provisional patent applications No. 60/212,301, filed Jun. 19, 2000, andSer. No. not yet assigned, filed Jun. 7, 2001, entitled “Line Selectionof Molecular Fluorine Laser Emission” by inventors Dr. Sergei Govorkov,Dr. Klaus Vogler and Mr. Rainer Paetzel.

BACKGROUND OF THE INVENTION

[0002] 1. Field of the Invention

[0003] The present invention relates to a method for adjusting thebandwidth of a natural or line-narrowed emission line of a F₂ laser(e.g., λ₁=157.63094 nm) by adjusting the gas mixture to a selectedcomposition.

[0004] 2. Discussion of the Related Art

[0005] Line-narrowing is an important feature of excimer laser systemsbeing used for optical lithography. Commonly the bandwidth of thenatural emission of the DUV or VUV laser being used is too broad to beused with projection illumination systems. A very small bandwidth isespecially valuable when using high numerical aperture (NA) refractiveimaging systems, wherein bandwidths below 1 pm are desired when the NAof the projection lens is very high, such as 70 or more. Line-narrowingof natural emission lines of excimer lasers is usually done bysophisticated dispersive arrangements within the laser resonator. Forexample, line-narrowing of the natural emission of the ArF laser isshown in U.S. Pat. No. 5,901,163 as being performed by a prism beamexpander-grating rear optics line-narrowing module in combination withan etalon outcoupler, and U.S. Pat. Nos. 6,154,470, 5,150,370,5,596,596, 5,642,374, 5,559,816, and 5,852,627, and EP 0 472 727 B1,which are hereby incorporated by reference into the present applicationin this discussion and in the discussion of the preferred embodiment asdisclosing variations of features of the preferred embodiment. All ofthese optical elements are expensive and suffer more or less fromdegradation due to exposure to the high intensity, intra-resonator UVemission of the laser. It is desired to have a narrow band laser,particularly for DUV and/or VUV microlithography, that has a naturalbandwidth that is less than 0.6 pm, i.e., without additionalintra-resonator line-narrowing optics, and/or has a bandwidth that isadjustable in a range from around 1 pm to 0.5 pm or less without havingto adjust any intra-resonator line-narrowing elements.

[0006] One laser that is coming into high prominence formicrolithography purposes is the molecular fluorine (F₂) laser emittingaround 157 nm. The value of the natural bandwidth of the F₂ laser to beused, as well as the feasibility and limits of adjusting the bandwidth,are considerations for optical imaging system designs for 157 nm waferillumination. It is desired, then, to have an F₂ laser system that iscapable of emitting at bandwidths that meet the specifications of theseoptical systems.

RECOGNIZED IN THE PRESENT INVENTION

[0007] It is recognized in the present invention that for bandwidthsfrom 0.6 to 1.0 pm, catadioptic projection systems are used. Forbandwidths less than around 0.5 to 0.6 pm, a second material may be used(e.g., BaF₂ along with CaF₂) for dichroic correction. For linewidthsless than, e.g., around 0.2 pm, an optical design based only on oneoptical material may be used. Currently, CaF₂ is the most available ofthese materials in high quality and volume. In addition, the smaller thenatural bandwidth of the laser, the easier it is to provide additionalline-narrowing optics to meet the specifications of particular opticalsystems.

[0008] It is recognized herein that the natural bandwidth of themolecular fluorine F₂ laser main emission line at λ₁ is around 0.6+/−0.1pm using a gas mixture of approximately F₂ (5% in Ne):He (buffer)=70mbar:2730 mbar. It is further recognized herein that that the bandwidthdepends on the definite gas mixture which is used as the laser activemedium for producing the F₂ laser emission. Especially, a remarkabledependence of the natural bandwidth on the total pressure within thelaser tube, or d(BW)/dP.

SUMMARY OF THE INVENTION

[0009] In view of the above, a molecular fluorine laser system isprovided including a discharge tube filled with a gas mixture includingmolecular fluorine and at least one buffer gas and having a totalpressure of less than substantially 2500 mbar, multiple electrodeswithin the discharge tube, a pulsed discharge circuit connected to theelectrodes for energizing the gas mixture, a line-selection optic forselecting one of multiple closely-spaced lines around 157 nm emittedfrom the discharge tube, and a laser resonator including theline-selection optic and the discharge tube for generating a beam oflaser pulses having a wavelength around 157 nm at a bandwidth of lessthan 0.6 pm.

[0010] A molecular fluorine laser system is further provided including adischarge tube filled with a gas mixture including molecular fluorineand at least one buffer gas and having a total pressure of less than2000 mbar, multiple electrodes within the discharge tube and connectedto a pulsed discharge circuit for energizing the gas mixture, aline-selection optic for selecting one of multiple closely-spaced linesaround 157 nm emitted from the discharge tube, and a laser resonatorincluding the line-selection optic and the discharge tube for generatinga laser beam having a wavelength around 157 nm at a bandwidth of lessthan 0.6 pm.

[0011] A molecular fluorine laser system is also provided including adischarge tube filled with a gas mixture including molecular fluorineand at least one buffer gas and having a total pressure of less thansubstantially 1500 mbar, multiple electrodes within the discharge tubeand connected to a pulsed discharge circuit for energizing the gasmixture, a line-selection optic for selecting one of multipleclosely-spaced lines around 157 nm emitted from the discharge tube, anda laser resonator including the line-selection optic and the dischargetube for generating a laser beam having a wavelength around 157 nm at abandwidth of less than 0.6 pm.

[0012] A molecular fluorine laser system is further provided including adischarge tube filled with a gas mixture including molecular fluorineand at least one buffer gas and having a total pressure of less thansubstantially 1000 mbar, multiple electrodes within the discharge tubeand connected to a pulsed discharge circuit for energizing the gasmixture, a line-selection optic for selecting one of multipleclosely-spaced lines around 157 nm emitted from the discharge tube, anda laser resonator including the line-selection optic and the dischargetube for generating a laser beam having a wavelength around 157 nm at abandwidth of less than 0.6 pm.

[0013] A molecular fluorine laser system is also provided including adischarge tube filled with a gas mixture including molecular fluorineand at least one buffer gas and having a total pressure of less thansubstantially 2500 mbar, multiple electrodes within the discharge tubeand connected to a pulsed discharge circuit for energizing the gasmixture, a line-narrowing module for selecting one of multipleclosely-spaced lines around 157 nm emitted from the discharge tube, andfor optically narrowing the bandwidth of the selected line, and a laserresonator including the line-narrowing module and the discharge tube forgenerating a beam of laser pulses having a wavelength around 157 nm at abandwidth of less than 0.5 pm.

[0014] A molecular fluorine laser system is further provided including adischarge tube filled with a gas mixture including molecular fluorineand at least one buffer gas and having a total pressure of less than2000 mbar, multiple electrodes within the discharge tube and connectedto a pulsed discharge circuit for energizing the gas mixture, aline-narrowing module for selecting one of multiple closely-spaced linesaround 157 nm emitted from the discharge tube, and for opticallynarrowing the bandwidth of the selected line, and a laser resonatorincluding the line-narrowing module and the discharge tube forgenerating a beam of laser pulses having a wavelength around 157 nm at abandwidth of less than 0.5 pm.

[0015] A molecular fluorine laser system is also provided including adischarge tube filled with a gas mixture including molecular fluorineand at least one buffer gas and having a total pressure of less thansubstantially 1500 mbar, multiple electrodes within the discharge tubeand connected to a pulsed discharge circuit for energizing the gasmixture, a line-narrowing module for selecting one of multipleclosely-spaced lines around 157 nm emitted from the discharge tube, andfor optically narrowing the bandwidth of the selected line, and a laserresonator including the line-narrowing module and the discharge tube forgenerating a beam of laser pulses having a wavelength around 157 nm at abandwidth of less than 0.5 pm.

[0016] A molecular fluorine laser system is further provided including adischarge tube filled with a gas mixture including molecular fluorineand at least one buffer gas and having a total pressure of less thansubstantially 1000 mbar, multiple electrodes within the discharge tubeand connected to a pulsed discharge circuit for energizing the gasmixture, a line-narrowing module for selecting one of multipleclosely-spaced lines around 157 nm emitted from the discharge tube, andfor optically narrowing the bandwidth of the selected line, and a laserresonator including the line-narrowing module and the discharge tube forgenerating a beam of laser pulses having a wavelength around 157 nm at abandwidth of less than 0.5 pm.

[0017] A molecular fluorine laser system is also provided including adischarge tube filled with a gas mixture including molecular fluorineand at least one buffer gas and having a total pressure of less thansubstantially 2500 mbar, multiple electrodes within the discharge tubeand connected to a pulsed discharge circuit for energizing the gasmixture, a line-selection optic for selecting one of multipleclosely-spaced lines around 157 nm emitted from the discharge tube, alaser resonator including the line-selection optic and the dischargetube for generating a beam of laser pulses having a wavelength around157 nm at a bandwidth of less than 0.6 pm, and an amplifier for boostingthe energies of the laser pulses to desired energies forphotolithographic processing.

[0018] A molecular fluorine laser system is also provided including adischarge tube filled with a gas mixture including molecular fluorineand at least one buffer gas and having a total pressure of less thansubstantially 2000 mbar, multiple electrodes within the discharge tubeand connected to a pulsed discharge circuit for energizing the gasmixture, a line-selection optic for selecting one of multipleclosely-spaced lines around 157 nm emitted from the discharge tube, alaser resonator including the line-selection optic and the dischargetube for generating a beam of laser pulses having a wavelength around157 nm at a bandwidth of less than 0.6 pm, and an amplifier for boostingthe energies of the laser pulses to desired energies forphotolithographic processing.

[0019] A molecular fluorine laser system is further provided including adischarge tube filled with a gas mixture including molecular fluorineand at least one buffer gas and having a total pressure of less thansubstantially 1500 mbar, multiple electrodes within the discharge tubeand connected to a pulsed discharge circuit for energizing the gasmixture, a line-selection optic for selecting one of multipleclosely-spaced lines around 157 nm emitted from the discharge tube, alaser resonator including the line-selection optic and the dischargetube for generating a beam of laser pulses having a wavelength around157 nm at a bandwidth of less than 0.6 pm, and an amplifier for boostingthe energies of the laser pulses to desired energies forphotolithographic processing.

[0020] A molecular fluorine laser system is also provided including adischarge tube filled with a gas mixture including molecular fluorineand at least one buffer gas and having a total pressure of less thansubstantially 1000 mbar, multiple electrodes within the discharge tubeand connected to a pulsed discharge circuit for energizing the gasmixture, a line-selection optic for selecting one of multipleclosely-spaced lines around 157 nm emitted from the discharge tube, alaser resonator including the line-selection optic and the dischargetube for generating a beam of laser pulses having a wavelength around157 nm at a bandwidth of less than 0.6 pm, and an amplifier for boostingthe energies of the laser pulses to desired energies forphotolithographic processing.

[0021] A molecular fluorine laser system is further provided including adischarge tube filled with a gas mixture including molecular fluorineand at least one buffer gas, multiple electrodes within the dischargetube, a pulsed discharge circuit connected to the electrodes forenergizing the gas mixture, a line-selection optic for selecting one ofmultiple closely-spaced lines around 157 nm emitted from the dischargetube, a laser resonator including the line-selection optic and thedischarge tube for generating a beam of laser pulses having a wavelengtharound 157 nm at a bandwidth of less than 0.6 pm, a diagnostic modulefor measuring spectral information of the laser pulses, a processor forreceiving diagnostic signals containing the spectral information fromthe diagnostic module, and a gas handling unit for receiving instructionsignals from the processor and for adjusting the gas mixture based oninformation contained in the instruction signals.

[0022] A molecular fluorine laser system is further provided including adischarge tube filled with a gas mixture including molecular fluorineand at least one buffer gas and having a total pressure of less thansubstantially 2500 mbar, multiple electrodes within the discharge tube,a pulsed discharge circuit connected to the electrodes for energizingthe gas mixture, a line-selection optic for selecting one of multipleclosely-spaced lines around 157 nm emitted from the discharge tube, alaser resonator including the line-selection optic and the dischargetube for generating a beam of laser pulses having a wavelength around157 nm at a bandwidth of less than 0.6 pm, a diagnostic module formeasuring the bandwidth of the laser pulses, a processor for receivingdiagnostic signals containing bandwidth information from the diagnosticmodule, and a gas handling unit for receiving instruction signals fromthe processor and for adjusting the total pressure of the gas mixturebased on information contained in the instruction signals to control thebandwidth of the laser pulses.

BRIEF DESCRIPTION OF THE DRAWINGS

[0023]FIG. 1 shows a molecular fluorine laser system in accord with apreferred embodiment.

[0024]FIG. 2 shows a molecular fluorine laser system including anauxiliary volume in accord with a preferred embodiment.

[0025]FIG. 3 shows the natural bandwidth of an F₂ laser measured with ahigh resolution vacuum etalon spectrometer.

[0026]FIG. 4a shows a pressure dependence of the bandwidth in a pressurerange from 1500 mbar to 4000 mbar using the high resolution etalonspectrometer, and a CCD array, used to obtain the spectrum of FIG. 3.

[0027]FIG. 4b shows a pressure dependence of the bandwidth in a pressurerange from 0 mbar to 5000 mbar indicating a linear dependence of thebandwidth on the total gas pressure in the F₂ laser tube.

[0028]FIG. 5 shows a fringe pattern of high resolution VUV etalonspectrometer for measuring a line-narrowed bandwidth of an F₂ laserusing intracavity line-narrowing optics.

[0029]FIG. 6 the F₂ partial pressure dependence of the pulse energy fora F₂ laser.

[0030]FIG. 7 shows that there is no appreciable dependence of thebandwidth on the input operating high voltage to the laser dischargeelectrodes.

[0031]FIG. 8 shows output power of a F₂ laser beam as a function of therepetition rate for the pulsed discharge.

[0032]FIG. 9 shows the dependence of the bandwidth of an F₂ lasernatural emission on the partial pressure of F₂ in the gas mixture andthe total pressure of the gas mixture.

[0033]FIG. 10 shows bandwidth dependences of natural emissions of the F₂laser on the gas composition, wherein the amount of Ne in the mixturewas varied and the total pressure was varied.

[0034]FIG. 11 lists related references and a table of bandwidthsmeasured by the authors of these references.

INCORPORATION BY REFERENCE

[0035] What follows is a cite list of references each of which is, inaddition to those references cited above in the priority section, herebyincorporated by reference into the detailed description of the preferredembodiment below, as disclosing alternative embodiments of elements orfeatures of the preferred embodiments not otherwise set forth in detailbelow. A single one or a combination of two or more of these referencesmay be consulted to obtain a variation of the preferred embodimentsdescribed in the detailed description below. Further patent, patentapplication and non-patent references are cited in the writtendescription and are also incorporated by reference into the preferredembodiment with the same effect as just described with respect to thefollowing references:

[0036] U.S. patent application Ser. Nos. 09/453,670, 09/447,882,09/317,695, 09/574,921, 09/512,417, 09/599,130, 09/694,246, 09/712,877,09/738,849, 09/718,809, 09/733,874, and 09/780,124, each of which isassigned to the same assignee as the present application; and

[0037] U.S. Pat. Nos. 6,154,470, 6,157,662, 6,219,368, and 5,901,163,and all patent, patent application and non-patent references mentionedin the background or specification of this application.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0038] The preferred embodiments described below are drawn to a F₂ laserhaving a variably adjustable total gas pressure for adjusting thebandwidth of the laser emission around 157 nm. A F₂ laser is providedwith a controlled total gas pressure, which is preferably below atypical excimer laser total laser tube gas pressure, for controlling thenatural bandwidth of the laser emission around 157 nm, e.g., tosubstantially 0.5 pm or less. For example, the total pressure may bepreferably below 2000 mbar and may be below 1500 mbar and may be below1000 mbar. The F₂ partial pressure is preferably maintained at a desiredamount such as 50 to 100 mbar (5% F₂: 95% Ne), or 2 to 5 mbar F₂, whilethe remainder of the gas mixture is buffer gas. The total gas pressureis preferably controlled by controlling the partial pressure of thebuffer gas in the gas mixture, wherein He and/or Ne is/are the preferredbuffer gas or gases. Also preferably, the power or energy of thenarrow-band output laser beam is boosted by being directed through anoptical amplifier or increasing the driving voltage applied to thedischarge electrodes, or otherwise as understood by those skilled in theart. Preferably and advantageously, the optical design of the resonatorof the laser has minimal optical components that tend to significantlydegrade under VUV light exposure.

[0039] Referring to FIG. 1, an excimer or molecular fluorine lasersystem is schematically shown according to a preferred embodiment. Thepreferred gas discharge laser system is a VUV laser system, such as amolecular fluorine (F₂) laser system, for use with a vacuum ultraviolet(VUV) lithography system. Alternative configurations for laser systemsfor use in such other industrial applications as TFT annealing,photoablation and/or micromachining, e.g., include configurationsunderstood by those skilled in the art as being similar to and/ormodified from the system shown in FIG. 1 to meet the requirements ofthat application. For this purpose, alternative DUV or VUV laser systemand component configurations are described at U.S. patent applicationSer. Nos. 09/317,695, 09/130,277, 09/244,554, 09/452,353, 09/512,417,09/599,130, 09/694,246, 09/712,877, 09/574,921, 09/738,849, 09/718,809,09/629,256, 09/712,367, 09/771,366, 09/715,803, 09/738,849, 60/202,564,60/204,095, 09/741,465, 09/574,921, 09/734,459, 09/741,465, 09/686,483,09/715,803, and 09/780,124, and U.S. Pat. Nos. 6,005,880, 6,061,382,6,020,723, 5,946,337, 6,014,206, 6,157,662, 6,154,470, 6,160,831,6,160,832, 5,559,816, 4,611,270, 5,761,236, 6,212,214, 6,154,470, and6,157,662, each of which is assigned to the same assignee as the presentapplication and is hereby incorporated by reference.

[0040] The system shown in FIG. 1 generally includes a laser chamber 102(or laser tube including a heat exchanger and fan for circulating a gasmixture within the chamber 102 or tube) having a pair of main dischargeelectrodes 103 connected with a solid-state pulser module 104, and a gashandling module 106. The gas handling module 106 has a valve connectionto the laser chamber 102 so that halogen, rare and buffer gases, andpreferably a gas additive, may be injected or filled into the laserchamber, preferably in premixed forms (see U.S. patent application SerNo. 09/513,025, which is assigned to the same assignee as the presentapplication, and U.S. Pat. No. 4,977,573, which are each herebyincorporated by reference) for ArF, XeCl and KrF excimer lasers, andhalogen and buffer gases, and any gas additive, for the F₂ laser. Forthe high power XeCl laser, the gas handling module may or may not bepresent in the overall system. The solid-state pulser module 104 ispowered by a high voltage power supply 108. A thyratron pulser modulemay alternatively be used. The laser chamber 102 is surrounded by opticsmodule 110 and optics module 112, forming a resonator. The optics modulemay include only a highly reflective resonator reflector in the rearoptics module 110 and a partially reflecting output coupling mirror inthe front optics module 112, such as is preferred for the high powerXeCl laser. The optics modules 110 and 112 may be controlled by anoptics control module 114, or may be alternatively directly controlledby a computer or processor 116, particular when line-narrowing opticsare included in one or both of the optics modules 110, 112, such as ispreferred when KrF, ArF or F₂ lasers are used for optical lithography.

[0041] The processor 116 for laser control receives various inputs andcontrols various operating parameters of the system. A diagnostic module118 receives and measures one or more parameters, such as pulse energy,average energy and/or power, and preferably wavelength, of a split offportion of the main beam 120 via optics for deflecting a small portionof the beam toward the module 118, such as preferably a beam splittermodule 122. The beam 120 is preferably the laser output to an imagingsystem (not shown) and ultimately to a workpiece (also not shown) suchas particularly for lithographic applications, and may be outputdirectly to an application process. The laser control computer 116 maycommunicate through an interface 124 with a stepper/scanner computer,other control units 126, 128 and/or other external systems.

[0042] The laser chamber 102 contains a laser gas mixture and includesone or more preionization electrodes (not shown) in addition to the pairof main discharge electrodes 103. Preferred main electrodes 103 aredescribed at U.S. patent application Ser. No. 09/453,670 forphotolithographic applications, which is assigned to the same assigneeas the present application and is hereby incorporated by reference, andmay be alternatively configured, e.g., when a narrow discharge width isnot preferred. Other electrode configurations are set forth at U.S. Pat.Nos. 5,729,565 and 4,860,300, each of which is assigned to the sameassignee, and alternative embodiments are set forth at U.S. Pat. Nos.4,691,322, 5,535,233 and 5,557,629, all of which are hereby incorporatedby reference. Preferred preionization units are set forth at U.S. patentapplication Ser. Nos. 09/692,265 (particularly preferred for KrF, ArF,F₂ lasers), 09/532,276 and 09/247,887, each of which is assigned to thesame assignee as the present application, and alternative embodimentsare set forth at U.S. Pat. Nos. 5,337,330, 5,818,865 and 5,991,324, allof the above patents and patent applications being hereby incorporatedby reference.

[0043] The solid-state or thyratron pulser module 104 and high voltagepower supply 108 supply electrical energy in compressed electricalpulses to the preionization and main electrodes 103 within the laserchamber 102 to energize the gas mixture. Components of the preferredpulser module and high voltage power supply may be described at U.S.patent application Ser. Nos. 09/640,595, 60/198,058, 60/204,095,09/432,348 and 09/390,146, and 60/204,095, and U.S. Pat. Nos. 6,005,880,6,226,307 and 6,020,723, each of which is assigned to the same assigneeas the present application and which is hereby incorporated by referenceinto the present application. Other alternative pulser modules aredescribed at U.S. Pat. Nos. 5,982,800, 5,982,795, 5,940,421, 5,914,974,5,949,806, 5,936,988, 6,028,872, 6,151,346 and 5,729,562, each of whichis hereby incorporated by reference.

[0044] The laser resonator which surrounds the laser chamber 102containing the laser gas mixture includes optics module 110 preferablyincluding line-narrowing optics for a line narrowed excimer or molecularfluorine laser such as for photolithography, which may be replaced by ahigh reflectivity mirror or the like in a laser system wherein eitherline-narrowing is not desired (for TFT annealling, e.g.), or if linenarrowing is performed at the front optics module 112, or a spectralfilter external to the resonator is used, or if the line-narrowingoptics are disposed in front of the HR mirror, for narrowing thebandwidth of the output beam. In accord with a preferred embodimentherein, optics for selecting one of multiple lines around 157 nm may beused, e.g., one or more dispersive prisms or birefringent plates orblocks, wherein additional line-narrowing optics for narrowing theselected line may be left out. The total gas mixture pressure ispreferably lower than conventional systems, e.g., lower than 3 bar, forproducing the selected line at a narrow bandwidth such as 0.5 pm or lesswithout using additional line-narrowing optics.

[0045] The laser chamber 102 is sealed by windows transparent to thewavelengths of the emitted laser radiation 120. The windows may beBrewster windows or may be aligned at another angle, e.g., 5°, to theoptical path of the resonating beam. One of the windows may also serveto output couple the beam or as a highly reflective resonator reflectoron the opposite side of the chamber 102 as the beam is outcoupled.

[0046] After a portion of the output beam 120 passes the outcoupler ofthe optics module 112, that output portion preferably impinges upon abeam splitter module 122 which includes optics for deflecting a portionof the beam to the diagnostic module 118, or otherwise allowing a smallportion of the outcoupled beam to reach the diagnostic module 118, whilea main beam portion 120 is allowed to continue as the output beam 120 ofthe laser system (see U.S. patent application Ser Nos. 09/771,013,09/598,552, and 09/712,877 which are assigned to the same assignee asthe present invention, and U.S. Pat. No. 4,611,270, each of which ishereby incorporated by reference. Preferred optics include abeamsplitter or otherwise partially reflecting surface optic. The opticsmay also include a mirror or beam splitter as a second reflecting optic.More than one beam splitter and/or HR mirror(s), and/or dichroicmirror(s) may be used to direct portions of the beam to components ofthe diagnostic module 118. A holographic beam sampler, transmissiongrating, partially transmissive reflection diffraction grating, grism,prism or other refractive, dispersive and/or transmissive optic oroptics may also be used to separate a small beam portion from the mainbeam 120 for detection at the diagnostic module 118, while allowing mostof the main beam 120 to reach an application process directly or via animaging system or otherwise. These optics or additional optics may beused to filter out visible radiation such as the red emission fromatomic fluorine in the gas mixture from the split off beam prior todetection.

[0047] The output beam 120 may be transmitted at the beam splittermodule while a reflected beam portion is directed at the diagnosticmodule 118, or the main beam 120 may be reflected, while a small portionis transmitted to the diagnostic module 118. The portion of theoutcoupled beam which continues past the beam splitter module is theoutput beam 120 of the laser, which propagates toward an industrial orexperimental application such as an imaging system and workpiece forphotolithographic applications.

[0048] Particularly for the molecular fluorine laser system, and for theArF laser system, an enclosure (not shown) preferably seals the beampath of the beam 120 such as to keep the beam path free ofphotoabsorbing species. Smaller enclosures preferably seal the beam pathbetween the chamber 102 and the optics modules 110 and 112 and betweenthe beam splitter 122 and the diagnostic module 118. Preferredenclosures are described in detail in U.S. patent application Ser. Nos.09/598,552, 09/594,892 and 09/131,580, which are assigned to the sameassignee and are hereby incorporated by reference, and U.S. Pat. Nos.6,219,368, 5,559,584, 5,221,823, 5,763,855, 5,811,753 and 4,616,908, allof which are hereby incorporated by reference.

[0049] The diagnostic module 118 preferably includes at least one energydetector. This detector measures the total energy of the beam portionthat corresponds directly to the energy of the output beam 120 ( seeU.S. Pat. Nos. 4,611,270 and 6,212,214 which are hereby incorporated byreference). An optical configuration such as an optical attenuator,e.g., a plate or a coating, or other optics may be formed on or near thedetector or beam splitter module 122 to control the intensity, spectraldistribution and/or other parameters of the radiation impinging upon thedetector (see U.S. patent application Ser. Nos. 09/172,805, 09/741,465,09/712,877, 09/771,013 and 09/771,366, each of which is assigned to thesame assignee as the present application and is hereby incorporated byreference).

[0050] One other component of the diagnostic module 118 is preferably awavelength and/or bandwidth detection component such as a monitor etalonor grating spectrometer (see U.S. patent application Ser. Nos.09/416,344, 09/686,483, and 09/791,431, each of which is assigned to thesame assignee as the present application, and U.S. Pat. Nos. 4,905,243,5,978,391, 5,450,207, 4,926,428, 5,748,346, 5,025,445, 6,160,832,6,160,831 and 5,978,394, all of the above wavelength and/or bandwidthdetection and monitoring components being hereby incorporated byreference. In accord with a preferred embodiment herein, the bandwidthis monitored and controlled in a feedback loop including the processor116 and gas handling module 106. The total pressure of the gas mixturein the laser tube 102 is controlled to a particular value for producingan output beam at a particular bandwidth.

[0051] Other components of the diagnostic module may include a pulseshape detector or ASE detector, such as are described at U.S. patentapplication Ser. Nos. 09/484,818 and 09/418,052, respectively, each ofwhich is assigned to the same assignee as the present application and ishereby incorporated by reference, such as for gas control and/or outputbeam energy stabilization, or to monitor the amount of amplifiedspontaneous emission (ASE) within the beam to ensure that the ASEremains below a predetermined level, as set forth in more detail below.There may be a beam alignment monitor, e.g., such as is described atU.S. Pat. No. 6,014,206, or beam profile monitor, e.g., U.S. patentapplication Ser. No. 09/780,124, which is assigned to the same assignee,wherein each of these patent documents is hereby incorporated byreference.

[0052] The processor or control computer 116 receives and processesvalues of some of the pulse shape, energy, ASE, energy stability, energyovershoot for burst mode operation, wavelength, spectral purity and/orbandwidth, among other input or output parameters of the laser systemand output beam. The processor 116 also controls the line narrowingmodule to tune the wavelength and/or bandwidth or spectral purity, andcontrols the power supply and pulser module 104 and 108 to controlpreferably the moving average pulse power or energy, such that theenergy dose at points on the workpiece is stabilized around a desiredvalue. In addition, the computer 116 controls the gas handling module106 which includes gas supply valves connected to various gas sources.Further functions of the processor 116 such as to provide overshootcontrol, energy stability control and/or to monitor input energy to thedischarge, are described in more detail at U.S. patent application Ser.No. 09/588,561, which is assigned to the same assignee and is herebyincorporated by reference.

[0053] As shown in FIG. 1, the processor 116 preferably communicateswith the solid-state or thyratron pulser module 104 and HV power supply108, separately or in combination, the gas handling module 106, theoptics modules 110 and/or 112, the diagnostic module 118, and aninterface 124. These laser system components are also shown in FIG. 2. Aspecific energy control component 130 is also shown in FIG. 2 forcontrolling the energy supplied to the electrodes 103 by the pulser 104and power supply 108. The processor 116 may also control an auxiliaryvolume 126 (see U.S. patent application Ser. No. 09/780,120, which isassigned to the same assignee as the present application and is herebyincorporated by reference) which may be connected to a vacuum pump 128for releasing gases from the laser tube 102 for reducing a totalpressure in the tube 102 according to preferred embodiments set forth inmore detail below. The total pressure may be initially at the lowerpressure desired for producing a bandwidth of 5 pm or below, as ispreferred, and no auxiliary volume 126 may be used. The use of theauxiliary volume 126 however permits a wide range of pressures to becontrolled as the pressure in the laser tube 102, and rapid adjustmentsof the total pressure may be thereby made.

[0054] Total pressure adjustments in the form of releases of gases orreduction of the total pressure within the laser tube 102 are preferablyfacilitated by using the auxiliary volume 126. A valve is opened betweenthe auxiliary volume 126 and the gas mixture in the laser tube 102 whenthe auxiliary volume 126 is at lower pressure than the laser tube 102,preferably due to the vacuum pump 128 being connected to the auxiliaryvolume 126 before or during the pressure release. Total pressureadjustments in the form of increases in the total pressure may beperformed using the valves of the gas handling unit 106 and injectingcombinations of gases or only a single gas such as the buffer gas ofhelium, neon or a combination thereof. Total pressure adjustments may befollowed by gas composition adjustments if it is determined that, e.g.,other than the desired partial pressure of halogen gas is within thelaser tube 102 after the total pressure adjustment. Total pressureadjustments may also be performed after gas replenishment actions, andmay be performed in combination with smaller adjustments of the drivingvoltage to the discharge than would be made if no pressure adjustmentswere performed in combination.

[0055] The auxiliary volume 126 is connected to the laser tube 102 forreleasing gas from the laser tube 102 into the volume 126 based oncontrol signals received from the processor 116. The processor 116regulates the release of gases via a valve assembly to the auxiliaryvolume 126, and also regulates the delivery of gases or mixtures ofgases to the laser tube 102 via a valve assembly or system of valvesassociated with the gas handling unit 106.

[0056] The auxiliary volume 126 preferably includes a reservoir orcompartment having a known volume and preferably having a pressure gaugeattached for measuring the pressure in the auxiliary volume.Alternatively or in combination with the pressure gauge, a flow ratecontroller 132 allows the processor to control the flow rate of gasesfrom the tube 102 to the auxiliary volume 126, so that the processor maycontrol and/or determine precisely how much gas is being released or hasbeen released. The auxiliary volume 126 as well as the laser tube mayalso each have means, such as a thermocouple arrangement, for measuringthe temperature of the gases within the volume 126 and tube 102. Thecompartment may be a few to thousands of cm³ or so in volumetric size(the laser tube 102 may be around 30,000 to 50,000 cm³ volumetrically).

[0057] At least one valve is included for controlling the flow of gasesbetween the laser tube 102 and the auxiliary volume 126. Additionalvalves may be included therebetween. Another valve is also includedbetween the vacuum pump 128 and the auxiliary volume 126 for controllingaccess between the vacuum pump 128 and the auxiliary volume 126. Afurther valve or valves may be provided between either or both of thevacuum pump 128 and auxiliary volume 126 and the laser tube 102 and theauxiliary volume 126 for controlling the atmosphere in the linetherebetween, and an additional pump or the same vacuum pump 128 may beused to evacuate the line between the laser tube 102 and auxiliaryvolume 126 either directly or through the auxiliary volume 126.

[0058] Predetermined amounts of the gas mixture in the tube 102 arepreferably released into the auxiliary volume 126 from the laser tube102 for total pressure releases according to algorithms which provideinstructions to the processor 116 (see the Ser. No. 09/780,120application). This same auxiliary volume 126 may be used in partial,mini- or macro-gas replacement operations such as are set forth in theSer. No. 09/734,459 application, incorporated by reference above. As anexample, the gas handling unit 106 connected to the laser tube 102either directly or through an additional valve assembly, such as mayinclude a small compartment for regulating the amount of gas injected(see the '459 application), may include a gas line for injecting apremix A including 1%F₂:99% Ne (or 5% F₂:95% Ne, or another mixture),and another gas line for injecting a buffer gas of helium and/or neonfor a F₂ laser. Thus, by injecting premix A into the tube 102 via thevalve assembly, the fluorine concentration (for the F₂ laser, e.g.) inthe laser tube 102 may be replenished. Then, a certain amount of gas isreleased corresponding to the amount that was injected. Additional gaslines and/or valves may be used for injecting additional gas mixtures.New fills, partial and mini gas replacements and gas injectionprocedures, e.g., enhanced and ordinary micro-halogen injections, andany and all other gas replenishment actions are initiated and controlledby the processor 116 which controls valve assemblies of the gas handlingunit 106, laser tube 102, auxiliary volume 126 and vacuum pump 128 basedon various input information in a feedback loop.

[0059] An exemplary method according to the present invention is nextdescribed for accurately and precisely releasing gas from the laser tube102 into the auxiliary volume 126. It is noted that a similar procedurefor accurately and precisely replenishing gases including injection intothe laser tube 102 are preferably used for injecting small amounts ofgases such that significant output beam parameters are not significantlydisturbed, if at all, with each gas injection. For example, theprocessor 116, which is monitoring a parameter indicative of thefluorine concentration in the laser tube 102, may initiate amicro-halogen injection (μHI) when the processor 116 determines it istime to increase the halogen concentration in the gas mixture in thelaser tube 102 (further details of preferred gas replenishment actionsare described at the '459 application).

[0060] With respect to preferred total pressure releases according topreferred embodiments herein, the processor 116 determines that it istime for a pressure release. The processor 116 then sends a signal thatcauses a valve to open between the tube 102 and the volume 126 to gasesto flow from the tube 102 to the volume 126 either to a predeterminedpressure in the auxiliary volume 126 or according to a known flow rateand time that the valve is to be opened. Then, the valve is closed.Preferably, the pressure in the tube 102 after the release is determinedby either a pressure gauge on the tube 102 or by calculation using theknown amount of gas released and the amount of gas that was in the tube102 before the release. A valve between the vacuum pump 128 and theauxiliary volume 126 is then preferably opened allowing the gas in thevolume 126 to be pumped out of the volume.

[0061] If the pressure in the tube was 3 bar prior to the release, andthe release is such that the pressure in the auxiliary volume wasincreased to, e.g., around 3 bar after the release, then 0.5×[(volume ofauxiliary volume 126)/volume of laser tube 102] bar would be thepressure reduction in the tube 102 as a result of the release.Particular total pressure release or addition algorithms are set forthin the Ser. No. 09/780,120 application.

[0062] The above calculation may be performed by the processor 116 todetermine more precisely how much gas was released, or prior to therelease, the pressure in the auxiliary volume 126 may be set accordingto a calculation by the processor 116 concerning how much gas should bereleased based on the information received by the processor 116 and/orbased on pre-programmed criteria. Preferably, the auxiliary volume 126is pumped down such that a substantially zero pressure approximation maybe used, or a very low pressure as measured by a gauge measuring thepressure in the interior of the volume 126. A correction for differencein temperature between the gas in the tube 102 and the auxiliary volume126 may also be performed by the processor 116 for greater accuracy, orthe temperature within the auxiliary volume may be preset, e.g., to thetemperature within the laser tube 102.

[0063] There may be more than one auxiliary volume like the volume 126,as described above, each having different properties such as volumetricspace. For example, there may be two compartments, one for gasreplacement procedures and one for total pressure releases. There may bemore than two, for still further versatility in the amounts of gas to bereleased, and for adjusting driving voltage ranges corresponding todifferent gas action algorithms (see the '459 application).

[0064] The gas mixture lifetime may be advantageously increased by usinggas replenishment procedures as described herein. This discussion belowmay be supplemented by the description in any of U.S. patent applicationSer. Nos. 09/447,882, 09/734,459 and/or 09/780,120, which are assignedto the same assignee as the present application, and/or U.S. Pat. No.6,212,214, each of which is hereby incorporated by reference.

[0065] The laser gas mixture is initially filled into the laser chamber102 in a process referred to herein as a “new fills”. In such procedure,the laser tube is evacuated of laser gases and contaminants, andre-filled with an ideal gas composition of fresh gas. The gascomposition for a very stable excimer or molecular fluorine laser inaccord with the preferred embodiment uses helium or neon or a mixture ofhelium and neon as buffer gas(es), depending on the particular laserbeing used. Preferred gas compositions are described at U.S. Pat. Nos.4,393,405, 6,157,162 and 4,977,573 and U.S. patent application Ser. Nos.09/513,025, 09/447,882, 09/418,052, and 09/588,561, each of which isassigned to the same assignee and is hereby incorporated by referenceinto the present application. The concentration of the fluorine in thegas mixture may range from 0.003% to 1.00% , and is preferably around0.1% . An additional gas additive, such as a rare gas or otherwise, maybe added for increased energy stability, overshoot control and/or as anattenuator as described in the Ser. No. 09/513,025 applicationincorporated by reference above. Specifically, for the F2-laser, anaddition of xenon, krypton and/or argon may be used. The concentrationof xenon or argon in the mixture may range from 0.0001% to 0.1% . For anArF-laser, an addition of xenon or krypton may be used also having aconcentration between 0.0001% to 0.1% . For the KrF laser, an additionof xenon or argon may be used also having a concentration between0.0001% to 0.1% . Although the preferred embodiments herein areparticularly drawn to use with a F₂ laser, adjustments to the totalpressure may be performed for controlling the bandwidth of other systemssuch as ArF, KrF, and XeCl excimer lasers.

[0066] Halogen and rare gas injections, including micro-halogeninjections of, e.g., 1-3 milliliters of halogen gas, mixed with, e.g.,20-60 milliliters of buffer gas or a mixture of the halogen gas, thebuffer gas and a active rare gas, per injection for a total gas volumein the laser tube 102 of, e.g., 100 liters, total pressure adjustmentsand gas replacement procedures are performed using the gas handlingmodule 106 preferably including a vacuum pump, a valve network and oneor more gas compartments. The gas handling module 106 receives gas viagas lines connected to gas containers, tanks, canisters and/or bottles.Some preferred and alternative gas handling and/or replenishmentprocedures, other than as specifically described herein (see below), aredescribed at U.S. Pat. Nos. 4,977,573, 6,212,214 and 5,396,514 and U.S.patent application Ser. Nos. 09/447,882, 09/418,052, 09/734,459,09/513,025 and 09/588,561, each of which is assigned to the sameassignee as the present application, and U.S. Pat. Nos. 5,978,406,6,014,398 and 6,028,880, all of which are hereby incorporated byreference. A xenon gas supply may be included either internal orexternal to the laser system according to the '025 application,mentioned above.

[0067] Total pressure adjustments in the form of releases of gases orreduction of the total pressure within the laser tube 102 may also beperformed. Total pressure adjustments may be followed by gas compositionadjustments if it is determined that, e.g., other than the desiredpartial pressure of halogen gas is within the laser tube 102 after thetotal pressure adjustment. Total pressure adjustments may also beperformed after gas replenishment actions, and may be performed incombination with smaller adjustments of the driving voltage to thedischarge than would be made if no pressure adjustments were performedin combination.

[0068] Gas replacement procedures may be performed and may be referredto as partial, mini- or macro-gas replacement operations, or partial newfill operations, depending on the amount of gas replaced, e.g., anywherefrom a few milliliters up to 50 liters or more, but less than a newfill, such as are set forth in the Ser. No. 09/734,459 application,incorporated by reference above. As an example, the gas handling unit106 connected to the laser tube 102 either directly or through anadditional valve assembly, such as may include a small compartment forregulating the amount of gas injected (see the '459 application), mayinclude a gas line for injecting a premix A including 1% F₂:99% Ne, andanother gas line for injecting a premix B including 1% Kr:99% Ne, for aKrF laser. For an ArF laser, premix B would have Ar instead of Kr, andfor a F₂ laser premix B is not used. Thus, by injecting premix A andpremix B into the tube 102 via the valve assembly, the fluorine andkrypton concentrations (for the KrF laser, e.g.) in the laser tube 102,respectively, may be replenished. Then, a certain amount of gas isreleased corresponding to the amount that was injected. Additional gaslines and/or valves may be used for injecting additional gas mixtures.New fills, partial and mini gas replacements and gas injectionprocedures, e.g., enhanced and ordinary micro-halogen injections, suchas between 1 milliliter or less and 3-10 milliliters, and any and allother gas replenishment actions are initiated and controlled by theprocessor 116 which controls valve assemblies of the gas handling unit106 and the laser tube 102 based on various input information in afeedback loop. These gas replenishment procedures may be used incombination with gas circulation loops and/or window replacementprocedures to achieve a laser system having an increased servicinginterval for both the gas mixture and the laser tube windows.

[0069] A general description of the line-narrowing features ofembodiments of the laser system particularly for use withphotolithographic applications is provided here, followed by a listingof patent and patent applications being incorporated by reference asdescribing variations and features that may used within the scope of thepresent invention for providing an output beam with a high spectralpurity or bandwidth (e.g., below 1 pm and preferably 0.6 pm or less).These exemplary embodiments may be used for selecting the primary lineX₁ only, or may be used to provide additional line narrowing to thatprovided by controlling the total pressure. Exemplary line-narrowingoptics contained in the optics module 110 include a beam expander, anoptional interferometric device such as an etalon or otherwise asdescribed in the Ser. No. 09/715,803 application, incorporated byreference above, and a diffraction grating, which produces a relativelyhigh degree of dispersion, for a narrow band laser such as is used witha refractive or catadioptric optical lithography imaging system. Asmentioned above, the front optics module may include line-narrowingoptics as well (see the Ser. Nos. 09/715,803, 09/738,849, and 09/718,809applications, each being assigned to the same assignee and herebyincorporated by reference).

[0070] For a semi-narrow band laser such as is used with anall-reflective imaging system, the grating may be replaced with a highlyreflective mirror, and a lower degree of dispersion may be produced by adispersive prism. A semi-narrow band laser would typically have anoutput beam linewidth in excess of 1 pm and may be as high as 100 pm insome laser systems, depending on the characteristic broadband bandwidthof the laser.

[0071] The beam expander of the above exemplary line-narrowing optics ofthe optics module 110 preferably includes one or more prisms. The beamexpander may include other beam expanding optics such as a lens assemblyor a converging/diverging lens pair. The grating or a highly reflectivemirror is preferably rotatable so that the wavelengths reflected intothe acceptance angle of the resonator can be selected or tuned.Alternatively, the grating, or other optic or optics, or the entireline-narrowing module may be pressure tuned, such as is set forth in theSer. No. 09/771,366 application and the U.S. Pat. No. 6,154,470 patent,each of which is assigned to the same assignee and is herebyincorporated by reference. The grating may be used both for dispersingthe beam for achieving narrow bandwidths and also preferably forretroreflecting the beam back toward the laser tube. Alternatively, ahighly reflective mirror is positioned after the grating which receivesa reflection from the grating and reflects the beam back toward thegrating in a Littman configuration, or the grating may be a transmissiongrating. One or more dispersive prisms may also be used, and more thanone etalon may be used.

[0072] Depending on the type and extent of line-narrowing and/orselection and tuning that is desired, and the particular laser that theline-narrowing optics are to be installed into, there are manyalternative optical configurations that may be used. For this purpose,those shown in U.S. Pat. Nos. 4,399,540, 4,905,243, 5,226,050,5,559,816, 5,659,419, 5,663,973, 5,761,236, 6.081,542, 6,061,382,5,946,337, 5,095,492, 5,684,822, 5,835,520, 5,852,627, 5,856,991,5,898,725, 5,901,163, 5,917,849, 5,970,082, 5,404,366, 4,975,919,5,142,543, 5,596,596, 5,802,094, 4,856,018, 5,970,082, 5,978,409,5,999,318, 5,150,370 and 4,829,536, and German patent DE 298 22 090.3,and any of the patent applications mentioned above and below herein, maybe consulted to obtain a line-narrowing configuration that may be usedwith a preferred laser system herein, and each of these patentreferences is each hereby incorporated by reference into the presentapplication.

[0073] Optics module 112 preferably includes means for outcoupling thebeam 120, such as a partially reflective resonator reflector. The beam120 may be otherwise outcoupled such as by an intra-resonator beamsplitter or partially reflecting surface of another optical element, andthe optics module 112 would in this case include a highly reflectivemirror. The optics control module 114 preferably controls the opticsmodules 110 and 112 such as by receiving and interpreting signals fromthe processor 16, and initiating realignment or reconfigurationprocedures (see the '353, '695, '277, '554, and '527 applicationsmentioned above).

[0074] The preferred embodiments relate particularly to excimer andmolecular fluorine laser systems configured for adjustment of a totalpressure in the laser tube 102 by using gas handling procedures,including total pressure releases and increases, of the gas mixture inthe laser tube 102. The halogen and the rare gas concentrations aremaintained constant during laser operation by gas replenishment actionsfor replenishing the amount of halogen, rare gas and buffer gas in thelaser tube for KrF and ArF excimer lasers, and halogen and buffer gasfor molecular fluorine lasers, such that these gases are maintained in asame predetermined ratio as are in the laser tube 102 following a newfill procedure. In addition, gas injection actions such as μHIs asunderstood from the '882 application, mentioned above, may beadvantageously modified into micro gas replacement procedures, such thatthe increase in energy of the output laser beam may be compensated byreducing the total pressure. In contrast, or alternatively, conventionallaser systems would reduce the input driving voltage so that the energyof the output beam is at the predetermined desired energy. In this way,the driving voltage is maintained within a small range around HV_(opt),while the gas procedure operates to replenish the gases and maintain theaverage pulse energy or energy dose, such as by controlling an outputrate of change of the gas mixture or a rate of gas flow through thelaser tube 102. Advantageously, the gas procedures set forth hereinpermit the laser system to operate within a very small range aroundHV_(opt), while still achieving average pulse energy control and gasreplenishment, and increasing the gas mixture lifetime or time betweennew fills.

[0075] The laser chamber 102 contains a laser gas mixture includingmolecular fluorine and one or more buffer gases, wherein the totalpressure may be adjusted to a predetermined pressure to adjust thebandwidth of the laser emission, as discussed in more detail below.Preferably and advantageously, the preferred embodiment does not haveadditional line-narrowing optics in the laser resonator, or includesonly line-selection optics for selecting the main line at λ₁≈157.63094nm and suppressing any other lines around 157 nm that may be naturallyemitted by the F₂ laser. Therefore, in one embodiment, the optics module110 has only a highly reflective resonator mirror, and the optics module112 has only a partially reflective resonator reflector. In anotherembodiment, suppression of the other lines (i.e., other than λ₁) around157 nm is performed by an outcoupler having a partially reflective innersurface and being made of a block of birefringent material or a VUVtransparent block with a coating, either of which has a transmissionspectrum which is periodic due to interference and/or birefringence, andhas a maximum at λ₁ and a minimum at a secondary line. In anotherembodiment, simple optics such as a dispersive prism or prisms may beused for line-selection only, and not for narrowing of the main line atλ₁. The advantageous gas mixture composition of the preferred embodimentenables a narrow bandwidth, e.g., substantially 5 pm or below 0.5 pmwithout narrowing the free-running main line at λ₁ using additionaloptics.

[0076] The processor 116 receives values of the bandwidth from thespectrometer of the diagnostic module 118 and controls the totalpressure in the discharge chamber 102 in conjunction with the gashandling module 106 to provide a stable and selected bandwidth of theoutput beam. The laser gas mixture is initially filled into the laserchamber 102 during new fills. The gas composition for a very stableexcimer laser in accord with the preferred embodiment uses helium orneon or a mixture of helium and neon as buffer gas, depending on thelaser. Preferably, a mixture of 5% (or less) F₂ in Ne with He as theremaining buffer gas in the discharge chamber 102 is used. The total gaspressure is advantageously adjustable between around 1500 and 4000 mbarfor adjusting the bandwidth of the laser. The total pressure may befurther reduced below 1500 mbar to perhaps as low as 1000 mbar, or evenlower. The partial pressure of the He buffer gas is preferably adjustedto adjust the total pressure, such that the amount of molecular fluorinein the laser tube 102 is not varied from an optimal, pre-selectedamount.

[0077]FIG. 3 shows the natural bandwidth of an F₂ laser measured with ahigh resolution vacuum etalon spectrometer. The spectrometer had anapparatus function f=around 0.1 pm. The laser system used to measure thedata for making the plot of FIG. 3 was F₂ (5% in Ne): balance He,wherein the total pressure was around 3000 mbar. The spectral width orbandwidth of the single emission line was determined from the data shownin the graph of FIG. 3 to be 0.6 pm+/−0.1 pm, and the energy of the beammeasured was 10 mJ. Although this energy is around that which is desiredfor photolithographic applications, the bandwidth is above that which isdesired herein.

[0078]FIG. 4a shows the total gas mixture pressure dependence of thebandwidth in a pressure range from 1500 pm to 4000 pm using the highresolution etalon spectrometer, and a CCD array, the same or similar tothat used to obtain the graph of FIG. 3. Four gas mixes were used havingvarying F₂ contents: the first around 20 mbar F₂ (5% in Ne), the secondaround 50 mbar F₂ (5% in Ne), the third around 80 mbar F₂ (5% in Ne) andthe fourth around 100 mbar (5% F₂in Ne), with the remainder of the gasin the gas mixture being He buffer gas. Although the vertical axis inFIG. 4a is measured in pixels on the CCD array, the correspondingbandwidths measured may be easily determined based on the dispersiveresolution of the spectrometer being around 0.082 pm/pixel. The generaltrend of reducing bandwidth with reduced total pressure is easilyobserved in FIG. 4a.

[0079]FIG. 4b shows a pressure dependence of the bandwidth in a pressurerange from 0 mbar to 5000 mbar indicating a linear dependence of thebandwidth on the total gas pressure in the F₂ laser tube. FIG. 4b showsthat at a total pressure of 0 mbar, the bandwidth is 0 mbar, and at atotal pressure of less than 2500 mbar, the bandwidth is less than around0.7 pm, and at a total pressure of less than 2000 mbar, the bandwidth isless than around 0.6 pm, and at a total pressure of less than 1500 mbar,the bandwidth is less than around 0.4 pm, and at a total pressure ofless than 1000 mbar, the bandwidth is less than around 0.3 pm, and at atotal pressure of less than 500 mbar, the bandwidth is less than around0.15 pm. As mentioned above, the trade-off for reducing the totalpressure and achieving an advantageously smaller bandwidth is loss ofenergy that may be compensated using an amplifier or increasing thedriving voltage, varying the amount of fluorine in the laser tube,varying the reflectivity of the outcoupler, perhaps increasing therepetition rate (to increase the energy dose per time), lengthening theelectrodes, etc. Also, the bandwidth may be maintained just at aspecified bandwidth, and not below even though the pressure could bereduced to achieve a lower bandwidth than is specified, in order tomaintain the energy at a specified level. A balancing analysis isperformed, and the flexibility of being able to select a bandwidth andthen adjust the system to maintain the specified energy is highlyadvantageous.

[0080] The pressure dependence from an observation of the plot of FIG.4a was around d(bandwidth)/d(total pressure) ≈0.1 pm/bar, although thedependence appeared to be greater, e.g., 1.5 pm/bar, at total pressuresbelow around 2500 mbar. With respect to the vertical axis, 8.5 pixelscorresponds to a bandwidth around 0.70 pm, 7.0 pixels to around 0.58 pm,and 10 pixels to around 0.82 pm. From these preliminary data, it isexpected that a bandwidth less than 0.4 pm would be achieved using 1000mbar total pressure in the gas mix, preferably with around 50 mbar F₂(5% in Ne): remainder He (or around 950 mbar He). A bandwidth of around0.5 pm or less is achieved using 2 bar total pressure in the gas mix. Asillustrated in both FIGS. 3 and 4a-4 b, a bandwidth around 0.6 pm isachieved with a gas pressure of 3 bar. FIG. 4b shows a bandwidthdependence on the total pressure of around 0.3 pm/bar, illustrating thatthe pressure dependence may vary with other laser conditions and/orparameters.

[0081]FIG. 5 shows the line-narrowed bandwidth of an F₂ laser usingintracavity line-narrowing optics. The intracavity line-narrowing opticsused in the resonator of the F₂ laser allowed a very narrow bandwidth ofless than around 0.15 pm. The energy of the beam was reduced to around 1mJ, which is below that which is desired for photolithographicapplications. Intracavity line-narrowing optics, such as those describedabove such as interferometric devices such as etalons or otherwise asset forth in the Ser. No. 09/715,803 application, or gratings, orgrisms, or combinations with dispersive prisms and preferably using abeam expander for lowering the divergence and expanding the beam priorto being dispersed, may be used to narrow the selected F₂,-laseremission line alternatively to, or in combination with, the use of lowtotal pressure, e.g., 1000 to 2500 mbar, to achieve a very narrowbandwidth. In a preferred embodiment herein, the low pressure is usedeither alone, i.e., with no intracavity line-narrowing, or incombination therewith. In each case, there is reduction in output energyfor a same input electrical energy to the discharge. In the case ofusing both lower pressure and intracavity line-narrowing optics, theenergy is reduced by both of these factors.

[0082]FIG. 6 illustrates the F₂ partial pressure dependence of the pulseenergy for an F₂ laser. The total pressure of the gas mixture of the F₂laser used to produce the graph of pulse energy versus F₂ partialpressure was maintained about constant at 1600 mbar. The graph in FIG. 6shows that for very low F₂ partial pressures, the pulse energy is quitelow. However, the pulse energy is not very much increased for addedfluorine to the gas mixture after about 100 mbar 5% F₂ in Ne. A pulseenergy of around 5.5 mJ was achieved at 1600 mbar total pressureincluding 100 mbar F₂ 5% in Ne with balance He.

[0083]FIG. 7 shows plots of linewidth or bandwidth of the selected F₂laser emission line at 3020 mbar total pressure, 80 mbar F₂ 5% in Ne andat 1510 mbar total pressure, 40 mbar F₂ 5% in Ne. The bandwidth is shownmeasured in pixels on the CCD array, which is proportional to thebandwidth in pm as described above with reference to FIG. 4. FIG. 7shows that the bandwidth is significantly reduced at 1510 mbar totalpressure as opposed to 3020 total pressure, but there is no appreciabledependence of the bandwidth on the input operating high voltage to thelaser discharge electrodes. It is known that the output energy of laserpulses will be increased as the driving voltage (HV) is increased. Thereduction in pulse energy incurred when the total pressure is reducedto, e.g., 1510 mbar, may be compensated according to a preferredembodiment by increasing the driving voltage to a higher level. Thepulser and power supply circuit described above would be modified todeliver the extra power.

[0084]FIG. 8 shows graphs of output power of a F₂ laser beam as afunction of the repetition rate of the pulsed discharge when the lasergas mixture is at 1500 mbar and at 3020 mbar. FIG. 8 shows that theoutput power at 200 Hz with a gas mixture of 80 mbar F₂ (5% in Ne):2940mbar He is four times greater than with a gas mixture of 100 mbar F₂ (5%in Ne):1400 mbar He, whereas at 50 Hz there is a smaller difference inpower. However, the difference appears to be about four times at each of50 Hz, 100 Hz, 150 Hz and 200 Hz. At higher repetition rates such as 1-2kHz or more, this difference of four times would result in an evenhigher power difference.

[0085] As mentioned above, some or all of this reduced power may becompensated by increasing the driving voltage, even if it entailsmodifying the discharge circuit. Alternatively, or in combination withincreasing the high voltage, the overall F₂ laser system may include anamplifier after the oscillator in accord with a preferred embodiment.The amplifier itself may be a discharge tube filed with a gas mixtureof, e.g., 1400-3400 mbar He buffer mixed with 100 mbar F₂ (5% in Ne). Inanother embodiment, the electrodes 103 of the system shown in FIGS. 1and 2 may be lengthened, e.g., to be greater than 28 inches long, suchas 30-40 inches or longer, as described in U.S. patent application Ser.No. 09/791,430, which is assigned to the same assignee as the presentapplication and is hereby incorporated by reference. The reflectivity ofthe partially reflecting outcoupling mirror may be increased in anotherembodiment, and a combination of these and/or other ways of increasingthe pulse energy may be used to bring the energy up to a desired energy,e.g., around 10 mJ, while the bandwidth is advantageously around 0.5 pmor less due to the low total pressure and/or intracavity line-narrowingoptics of the F₂ laser.

[0086]FIG. 9 shows the dependence of the bandwidth of the selected lineof an F₂ laser natural emission on the partial pressure of F₂ in the gasmixture and the total pressure of the gas mixture. The bandwidths at1500 mbar total pressure are clearly lower than those at each of 2500mbar, 3000 mbar and 4000 mbar. For example, at 1500 mbar total pressure,the bandwidth is around 6.7 to 7 pixels (0.55 pm to 0.58 pm), while thebandwidth at 4000 mbar total pressure is around 9 to 9.9 pixels (0.74 pmto 0.81 pm). FIG. 9 also shows that there is little dependence of thebandwidth on the F₂ partial pressure, while the high dependence of thebandwidth on the total pressure of the gas mixture is clearly observed.

[0087]FIG. 10 shows bandwidths of natural emissions of the F₂ laser onthe gas composition, wherein the amount of Ne in the mixture was variedand the total pressure was varied. FIG. 10 shows little or no dependenceof the bandwidth on the Ne partial pressure and a high dependence on thetotal pressure, as has been observed in earlier FIGS. 4 and 9 anddescribed above. FIG. 11 lists related references which are herebyincorporated by reference and a table of bandwidths measured by theauthors of these references.

[0088] The dependence of the bandwidth on the buffer gas or total gaspressure in the molecular fluorine laser tube has been shown, anddescribed above with particular reference to FIGS. 4, 9 and 10, toadvantageously decrease with decreased buffer gas in the gas mixture.Thus, the partial pressure of the buffer gas in the laser tube may beadjusted to adjust the bandwidth of the laser emission. In a preferredembodiment, the buffer gas pressure is maintained below ordinary totalpressures in excimer laser tubes, which are maintained, e.g., at 3 barto 5 bar. as described above, a reduction in total pressure of around 1bar reduces the bandwidth by around 0.1 pm.

[0089] Variations of gas compositions and supply techniques aredescribed at U.S. Pat. Nos. 4,393,405, 4,977,573 and 6,157,662 and U.S.patent application Ser. Nos. 09/513,025, 09/447,882 and 09/418,052, eachof which is assigned to the same assignee and is hereby incorporated byreference into the present application. The concentration of thefluorine in the gas mixture may range from 0.05 mbar to 30 mbar, and ispreferably around 3 mbar. Halogen and rare gas injections, totalpressure adjustments and gas replacement procedures are performed usingthe gas handling module 106 (see FIGS. 1-2) preferably including avacuum pump 128, a valve network and one or more gas compartments 126.The gas handling module 106 receives gas via gas lines connected to gascontainers, tanks, canisters and/or bottles. Preferred gas handlingand/or replenishment procedures of the preferred embodiment, other thanas specifically described herein, are described at U.S. Pat. Nos.4,977,573, 6,212,214 and 5,396,514 and U.S. patent application Ser. Nos.09/447,882, 09/418,052, 09/734,459, and 09/513,025, each of which isassigned to the same assignee as the present application, and U.S. Pat.Nos. 5,978,406, 6,014,398 and 6,028,880, all of which are herebyincorporated by reference. A rare gas supply may be included eitherinternal or external to the laser system according to the '025application, mentioned above, for adding trace amounts of a rare gas orrare gases for boosting the energy or more preferably for boosting theenergy stability and/or overshoot control of the laser.

[0090] As discussed, preferably there are no line-narrowing optics inthe resonator that are subject to degradation, wherein alternatively,only optics to select a single line (i.e., λ₁) may be used. However,line-narrowing optics may be used for further line-narrowing incombination with the line-narrowing and/or bandwidth adjustment that isperformed by adjusting/reducing the total pressure in the laser chamber.For example, a natural bandwidth may be adjusted to 0.5 pm by reducingthe buffer gas partial pressure to 1000-1500 mbar. The bandwidth couldthen be further reduced to 0.2 pm or below using line-narrowing opticseither in the resonator or external to the resonator. Thus, a generaldescription of the line-narrowing optics that may be used are providedabove.

[0091] In all of the above and below embodiments, the material used forthe prisms, either dispersive or of a beam expander, any etalons orother interferometric devices, laser windows and the outcoupler, ispreferably a material that is highly transparent at wavelengths below200 nm, such as at the 157 nm output emission wavelength of themolecular fluorine laser. The material is also capable of withstandinglong-term exposure to ultraviolet light with minimal degradationeffects. Examples of such materials are CaF₂, MgF₂, BaF2, LiF and SrF₂,wherein CaF₂ is generally preferred, and in some cases quartz orfluorine-doped quartz may be used. Also, in any of the embodiments,optical surfaces, particularly those of the prisms, may have ananti-reflective coating on one or more optical surfaces, in order tominimize reflection losses and prolong their lifetime.

[0092] A line-narrowed oscillator, e.g., a set forth above, may befollowed by a power amplifier for increasing the power of the beamoutput by the oscillator. Preferred features of the oscillator-amplifierset-up are set forth at U.S. patent application Ser. Nos. 09,1599,130and 60/228,184, which are assigned to the same assignee and are herebyincorporated by reference. The amplifier may be the same or a separatedischarge chamber 102 (see FIGS. 1-2). An optical or electrical delaymay be used to time the electrical discharge at the amplifier with thereaching of the optical pulse from the oscillator at the amplifier. Withparticular respect to the preferred embodiments herein, the molecularfluorine laser oscillator has an advantageous total gas pressure, or gascomposition, that produces a very narrow band emission at λ₁ withoutoptics that would otherwise be used for achieving such a very narrowbandwidth, e.g., less than 0.5 pm. A 157 nm beam is output from theoutput coupler and is incident at the amplifier of this embodiment toincrease the power of the beam. Thus, a very narrow bandwidth beam(e.g., less than 0.5 pm) is achieved with high power (at least severalWatts to more than 10 Watts), and such that 10 mJ, less than 0.6 pm, 157nm laser pulses are achieved, and without sophisticated very narrowbandwidth line-narrowing optics, or with such optics for having a laserpulses with bandwidths of 0.2 pm or less.

[0093] While exemplary drawings and specific embodiments of the presentinvention have been described and illustrated, it is to be understoodthat that the scope of the present invention is not to be limited to theparticular embodiments discussed. Thus, the embodiments shall beregarded as illustrative rather than restrictive, and it should beunderstood that variations may be made in those embodiments by workersskilled in the arts without departing from the scope of the presentinvention as set forth in the claims that follow, and equivalentsthereof.

[0094] In addition, in the method claims that follow, the operationshave been ordered in selected typographical sequences. However, thesequences have been selected and so ordered for typographicalconvenience and are not intended to imply any particular order forperforming the operations, except for those claims wherein a particularordering of steps is expressly set forth or understood by one ofordinary skill in the art as being necessary.

What is claimed is:
 1. A molecular fluorine laser system, comprising: adischarge tube filled with a gas mixture including molecular fluorineand at least one buffer gas and having a total pressure of less thansubstantially 2500 mbar; a plurality of electrodes within the dischargetube; a pulsed discharge circuit connected to the electrodes forenergizing the gas mixture; a line-selection optic for selecting one ofmultiple closely-spaced lines around 157 nm emitted from the dischargetube; and a laser resonator including the line-selection optic and thedischarge tube for generating a beam of laser pulses having a wavelengtharound 157 nm at a bandwidth of less than 0.6 pm.
 2. The laser system ofclaim 1, wherein the pulsed discharge circuit includes a power supplyfor supplying voltage pulses of at least 22 kV, such that the laserpulses have a desired energy for photolithographic processing.
 3. Thelaser system of claim 2, wherein the laser pulses have energies of atleast substantially 10 mJ.
 4. A molecular fluorine laser system,comprising: a discharge tube filled with a gas mixture includingmolecular fluorine and at least one buffer gas and having a totalpressure of less than 2000 mbar; a plurality of electrodes within thedischarge tube; a pulsed discharge circuit connected to the electrodesfor energizing the gas mixture; a line-selection optic for selecting oneof multiple closely-spaced lines around 157 nm emitted from thedischarge tube; and a laser resonator including the line-selection opticand the discharge tube for generating a laser beam having a wavelengtharound 157 nm at a bandwidth of less than 0.6 pm.
 5. The laser system ofclaim 4, wherein the pulsed discharge circuit includes a power supplyfor supplying voltage pulses of at least 22 kV, such that the laserpulses have a desired energy for photolithographic processing.
 6. Thelaser system of claim 5, wherein the laser pulses have energies of atleast substantially 10 mJ.
 7. A molecular fluorine laser system,comprising: a discharge tube filled with a gas mixture includingmolecular fluorine and at least one buffer gas and having a totalpressure of less than substantially 1500 mbar; a plurality of electrodeswithin the discharge tube; a pulsed discharge circuit connected to theelectrodes for energizing the gas mixture; a line-selection optic forselecting one of multiple closely-spaced lines around 157 nm emittedfrom the discharge tube; and a laser resonator including theline-selection optic and the discharge tube for generating a laser beamhaving a wavelength around 157 nm at a bandwidth of less than 0.6 pm. 8.The laser system of claim 7, wherein the pulsed discharge circuitincludes a power supply for supplying voltage pulses of at least 22 kV,such that the laser pulses have a desired energy for photolithographicprocessing.
 9. The laser system of claim 8, wherein the laser pulseshave energies of at least substantially 10 mJ.
 10. A molecular fluorinelaser system, comprising: a discharge tube filled with a gas mixtureincluding molecular fluorine and at least one buffer gas and having atotal pressure of less than substantially 1000 mbar; a plurality ofelectrodes within the discharge tube; a pulsed discharge circuitconnected to the electrodes for energizing the gas mixture; aline-selection optic for selecting one of multiple closely-spaced linesaround 157 nm emitted from the discharge tube; and a laser resonatorincluding the line-selection optic and the discharge tube for generatinga laser beam having a wavelength around 157 nm at a bandwidth of lessthan 0.6 pm.
 11. The laser system of claim 10, wherein the pulseddischarge circuit includes a power supply for supplying voltage pulsesof at least 22 kV, such that the laser pulses have a desired energy forphotolithographic processing.
 12. The laser system of claim 11, whereinthe laser pulses have energies of at least substantially 10 mJ.
 13. Amolecular fluorine laser system, comprising: a discharge tube filledwith a gas mixture including molecular fluorine and at least one buffergas and having a total pressure of less than substantially 2500 mbar; aplurality of electrodes within the discharge tube; a pulsed dischargecircuit connected to the electrodes for energizing the gas mixture; aline-narrowing module for selecting one of multiple closely-spaced linesaround 157 nm emitted from the discharge tube, and for opticallynarrowing the bandwidth of the selected line; and a laser resonatorincluding the line-narrowing module and the discharge tube forgenerating a beam of laser pulses having a wavelength around 157 nm at abandwidth of less than 0.5 pm.
 14. The laser system of claim 13, furthercomprising an amplifier for boosting the energies of the laser pulses todesired energies for photolithographic processing.
 15. The laser systemof claim 14, wherein said laser pulses have energies of at leastsubstantially 10 mJ.
 16. A molecular fluorine laser system, comprising:a discharge tube filled with a gas mixture including molecular fluorineand at least one buffer gas and having a total pressure of less than2000 mbar; a plurality of electrodes within the discharge tube; a pulseddischarge circuit connected to the electrodes for energizing the gasmixture; a line-narrowing module for selecting one of multipleclosely-spaced lines around 157 nm emitted from the discharge tube, andfor optically narrowing the bandwidth of the selected line; and a laserresonator including the line-narrowing module and the discharge tube forgenerating a beam of laser pulses having a wavelength around 157 nm at abandwidth of less than 0.5 pm.
 17. The laser system of claim 16, furthercomprising an amplifier for boosting the energies of the laser pulses todesired energies for photolithographic processing.
 18. The laser systemof claim 17, wherein said laser pulses have energies of at leastsubstantially 10 mJ.
 19. A molecular fluorine laser system, comprising:a discharge tube filled with a gas mixture including molecular fluorineand at least one buffer gas and having a total pressure of less thansubstantially 1500 mbar; a plurality of electrodes within the dischargetube; a pulsed discharge circuit connected to the electrodes forenergizing the gas mixture; a line-narrowing module for selecting one ofmultiple closely-spaced lines around 157 nm emitted from the dischargetube, and for optically narrowing the bandwidth of the selected line;and a laser resonator including the line-narrowing module and thedischarge tube for generating a beam of laser pulses having a wavelengtharound 157 nm at a bandwidth of less than 0.5 pm.
 20. The laser systemof claim 19, further comprising an amplifier for boosting the energiesof the laser pulses to desired energies for photolithographicprocessing.
 21. The laser system of claim 20, wherein said laser pulseshave energies of at least substantially 10 mJ.
 22. A molecular fluorinelaser system, comprising: a discharge tube filled with a gas mixtureincluding molecular fluorine and at least one buffer gas and having atotal pressure of less than substantially 1000 mbar; a plurality ofelectrodes within the discharge tube; a pulsed discharge circuitconnected to the electrodes for energizing the gas mixture; aline-narrowing module for selecting one of multiple closely-spaced linesaround 157 nm emitted from the discharge tube, and for opticallynarrowing the bandwidth of the selected line; and a laser resonatorincluding the line-narrowing module and the discharge tube forgenerating a beam of laser pulses having a wavelength around 157 nm at abandwidth of less than 0.5 pm.
 23. The laser system of claim 22, furthercomprising an amplifier for boosting the energies of the laser pulses todesired energies for photolithographic processing.
 24. The laser systemof claim 23, wherein said laser pulses have energies of at leastsubstantially 10 mJ.
 25. A molecular fluorine laser system, comprising:a discharge tube filled with a gas mixture including molecular fluorineand at least one buffer gas and having a total pressure of less thansubstantially 2500 mbar; a plurality of electrodes within the dischargetube; a pulsed discharge circuit connected to the electrodes forenergizing the gas mixture; a line-selection optic for selecting one ofmultiple closely-spaced lines around 157 nm emitted from the dischargetube; a laser resonator including the line-selection optic and thedischarge tube for generating a beam of laser pulses having a wavelengtharound 157 nm at a bandwidth of less than 0.6 pm; and an amplifier forboosting the energies of the laser pulses to desired energies forphotolithographic processing.
 26. The laser system of claim 23, whereinsaid laser pulses have energies of at least substantially 10 mJ.
 27. Amolecular fluorine laser system, comprising: a discharge tube filledwith a gas mixture including molecular fluorine and at least one buffergas and having a total pressure of less than substantially 2000 mbar; aplurality of electrodes within the discharge tube; a pulsed dischargecircuit connected to the electrodes for energizing the gas mixture; aline-selection optic for selecting one of multiple closely-spaced linesaround 157 nm emitted from the discharge tube; a laser resonatorincluding the line-selection optic and the discharge tube for generatinga beam of laser pulses having a wavelength around 157 nm at a bandwidthof less than 0.6 pm; and an amplifier for boosting the energies of thelaser pulses to desired energies for photolithographic processing. 28.The laser system of claim 27, wherein said laser pulses have energies ofat least substantially 10 mJ.
 29. A molecular fluorine laser system,comprising: a discharge tube filled with a gas mixture includingmolecular fluorine and at least one buffer gas and having a totalpressure of less than substantially 1500 mbar; a plurality of electrodeswithin the discharge tube; a pulsed discharge circuit connected to theelectrodes for energizing the gas mixture; a line-selection optic forselecting one of multiple closely-spaced lines around 157 nm emittedfrom the discharge tube; a laser resonator including the line-selectionoptic and the discharge tube for generating a beam of laser pulseshaving a wavelength around 157 nm at a bandwidth of less than 0.6 pm;and an amplifier for boosting the energies of the laser pulses todesired energies for photolithographic processing.
 30. The laser systemof claim 29, wherein said laser pulses have energies of at leastsubstantially 10 mJ.
 31. A molecular fluorine laser system, comprising:a discharge tube filled with a gas mixture including molecular fluorineand at least one buffer gas and having a total pressure of less thansubstantially 1000 mbar; a plurality of electrodes within the dischargetube; a pulsed discharge circuit connected to the electrodes forenergizing the gas mixture; a line-selection optic for selecting one ofmultiple closely-spaced lines around 157 nm emitted from the dischargetube; a laser resonator including the line-selection optic and thedischarge tube for generating a beam of laser pulses having a wavelengtharound 157 nm at a bandwidth of less than 0.6 pm; and an amplifier forboosting the energies of the laser pulses to desired energies forphotolithographic processing.
 32. The laser system of claim 23, whereinsaid laser pulses have energies of at least substantially 10 mJ.
 33. Amolecular fluorine laser system, comprising: a discharge tube filledwith a gas mixture including molecular fluorine and at least one buffergas; a plurality of electrodes within the discharge tube; a pulseddischarge circuit connected to the electrodes for energizing the gasmixture; a line-selection optic for selecting one of multipleclosely-spaced lines around 157 nm emitted from the discharge tube; alaser resonator including the line-selection optic and the dischargetube for generating a beam of laser pulses having a wavelength around157 nm at a bandwidth of less than 0.6 pm; a diagnostic module formeasuring spectral information of the laser pulses; a processor forreceiving diagnostic signals containing the spectral information fromthe diagnostic module; and a gas handling unit for receiving instructionsignals from the processor and for adjusting the gas mixture based oninformation contained in said instruction signals.
 34. The laser systemof claim 33, wherein the pulsed discharge circuit includes a powersupply for supplying voltage pulses of at least 22 kV, such that thelaser pulses have a desired energy for photolithographic processing. 35.The laser system of claim 34, wherein the laser pulses have energies ofat least substantially 10 mJ.
 36. The laser system of claim 33, furthercomprising an amplifier for boosting the energies of the laser pulses todesired energies for photolithographic processing.
 37. The laser systemof claim 34, wherein the laser pulses have energies of at leastsubstantially 10 mJ.
 38. A molecular fluorine laser system, comprising:a discharge tube filled with a gas mixture including molecular fluorineand at least one buffer gas and having a total pressure of less thansubstantially 2500 mbar; a plurality of electrodes within the dischargetube; a pulsed discharge circuit connected to the electrodes forenergizing the gas mixture; a line-selection optic for selecting one ofmultiple closely-spaced lines around 157 nm emitted from the dischargetube; a laser resonator including the line-selection optic and thedischarge tube for generating a beam of laser pulses having a wavelengtharound 157 nm at a bandwidth of less than 0.6 pm; a diagnostic modulefor measuring the bandwidth of the laser pulses; a processor forreceiving diagnostic signals containing bandwidth information from thediagnostic module; and a gas handling unit for receiving instructionsignals from the processor and for adjusting the total pressure of thegas mixture based on information contained in said instruction signalsto control the bandwidth of the laser pulses.
 39. The laser system ofclaim 38, wherein the pulsed discharge circuit includes a power supplyfor supplying voltage pulses of at least 22 kV, such that the laserpulses have a desired energy for photolithographic processing.
 40. Thelaser system of claim 39, wherein the laser pulses have energies of atleast substantially 10 mJ.
 41. The laser system of claim 38, furthercomprising an amplifier for boosting the energies of the laser pulses todesired energies for photolithographic processing.
 42. The laser systemof claim 34, wherein the laser pulses have energies of at leastsubstantially 10 mJ.